OBJECTIVES: 1) Studies on the mode of action of SPF, the rat liver protein which stimulates the microsome-associated transformation of squalene to squalene epoxide and of squalene epoxide to lanosterol. 2) Examination of sterol structure function relationships with model membranes, with the sterol-requiring bacterium Mycoplasma capricolum and the yeast sterol auxotroph GL7. 3) Studies on dual sterol functions in membranes with emphasis on the role of cholesterol in the control of phospholipid biosynthesis. 4) The functional significance of side-chain alkylation in the biosynthesis of yeast and plant sterols. The role of sterols in respiratory adaptation of yeast.